[2]
Note the difference between a front_insert_iterator and an
insert_iterator. It may seem that a front_insert_iterator is
the same as an insert_iterator constructed with an insertion
point that is the beginning of a sequence. In fact, though, there is
a very important difference: every assignment through a
front_insert_iterator corresponds to an insertion before the first
element of the sequence. If you are inserting elements at the
beginning of a sequence using an insert_iterator, then the elements
will appear in the order in which they were inserted. If, however,
you are inserting elements at the beginning of a sequence using a
front_insert_iterator, then the elements will appear in the reverse
of the order in which they were inserted.

[3]
Note how assignment through an front_insert_iterator is implemented.
In general, unary operator* must be defined so that it returns a
proxy object, where the proxy object defines operator= to perform
the insert operation. In this case, for the sake of simplicity, the
proxy object is the front_insert_iterator itself. That is, *i simply
returns i, and *i = t is equivalent to i = t. You should not,
however, rely on this behavior. It is an implementation detail,
and it is not guaranteed to remain the same in future versions.

[4]
This function exists solely for the sake of convenience:
since it is a non-member function, the template parameters may be
inferred and the type of the front_insert_iterator need not be declared
explicitly. One easy way to reverse a range and insert it
at the beginning of a Front Insertion SequenceS, for example, is
copy(first, last, front_inserter(S)).